The National Electric Code requires the telecommunications industry to provide electrical surge protection at the point of entry where external telecommunications lines enter a building. The code requires that telecommunications equipment (e.g. telephones, computers etc.) within the building be protected from three types of electrical hazards: 1) surge protection from lightning and switching surges; 2) over current protection; and 3) circuit lock-out protection for use in the event a disturbance remains on the circuit for an extended period of time.
The required protection is provided by installing a building entrance panel at the point where the outside telecommunications lines enter the building. The building entrance panel includes a surge protection module for each telecommunications circuit in the building so that each interior telecommunications circuit is protected from electrical disturbances on the external telecommunications lines. The building entrance panel further includes a means for over current protection.
Well-known surge protection modules have five (5) pins. When such a surge protection module is installed in a building entrance panel, two of its pins are in electrical communication with an interior telecommunications circuit, two of its pins are in electrical communication with the external telecommunications lines, and one of its pins is engaged with a ground terminal.
In general, there are three types of electrical surge protector modules available, notably analog surge protection modules that employ gas discharge tube (GDT) arrestors, digital surge protection modules that employ solid state arrestors, and hybrid surge protection modules that employ both GDT and solid state arrestors.
An example of a surge protection device having a modular construction so that a manufacturer can assemble the parts of the surge protection device in various combinations is disclosed in U.S. Pat. No. 6,608,899 to Spooner et al., assigned to Circa Telecom U.S.A., Ltd., the contents of which are incorporated by reference. The surge protection device includes a housing having a plurality of bores formed therein into which long pins and short pins are press fit and soldered for electrical communication with the external telecommunications lines and an internal telecommunications circuit, respectively. The housing further includes a pair of recesses into each of which may be press fit a positive temperature coefficient resistor. In one embodiment, spring clips help to hold the positive temperature coefficient resistors in place and provide needed electrical contacts. In a second embodiment, the spring clips further include an elongate part that extends to a test point opening formed in a cover of the surge protection device. The surge protection device may include either a gas discharge tube arrestor or a solid state arrestor, a fail safe device, an insulator member that is melted by the fail safe device when needed, and conductive shunt bars for use when the spring clips are not used.
Surge protection modules that employ GDT arrestors have proven to be reliable because of their ability to handle large surge currents while being resilient to extreme temperatures. Unfortunately, however, surge protection modules that employ GDT arrestors are too slow and imprecise for modern telecommunications equipment, which is sensitive to uncontrolled outside voltages.
Digital surge protection modules that employ solid state arrestors are more precise and faster than analog surge protection modules, and for their rated voltage range, are robust. However, if the rated current carrying capacity of the solid state arrestors is exceeded, digital surge protection modules suffer shortcomings. At extremely high current surges, digital surge protection modules will function once, then short to ground, after which, the digital surge protection modules must be replaced.
Hybrid surge protection modules that employ GDT and solid state arrestors in parallel combine the speed of response of solid state devices with the robustness of GDT devices. Typically, varistors are used in such hybrid surge protection modules because they can tolerate a high level of current as well as voltage spikes. Unfortunately, to-date such hybrid surge protection modules have proven to be slow, of limited durability and unsuitable for use in high-speed, high-bandwidth telecommunications circuits.
Some known surge protection modules also include protection for “sneak current”. Sneak current is unwanted, weak, but steady current which seeps into telecommunications circuits and can cause heating effects and damage over time. Voltage limiting devices such as GDT and solid state arrestors are not triggered by sneak current since sneak current is not associated with a high voltage, and thus, these types of voltage limiting devices do not shunt sneak current to ground. Typically, positive temperature coefficient (PTC) resistors are used in surge protection modules to protect downstream telecommunications equipment from sneak current.
Although existing surge protection modules offer adequate protection from electrical disturbances on external telecommunications lines, improved surge protection modules that are robust, resettable and suitable for protecting high-speed and high-bandwidth telecommunications circuits are desired. It is therefore an object of the present invention at least to provide a novel surge protection module.